1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus applicable to a recording apparatus such as a laser beam printer or the like.
2. Related Background Art
A printing apparatus such as a laser beam printer comprises, as known well, a controller for generating an image of a bit map for printing out print data outputted from a host device through a host I/F, a print engine for printing the image data outputted from the controller onto a form, and a power supply for supplying a power to the controller and the print engine. Major power consumption units in the printing apparatus are an execution processing unit and a memory unit in the controller, and a fixing unit heater and a drive motor in the print engine.
In this type of printing apparatus, the power supply is turned on and off by a single power switch to the power supply which supplies power to the controller and the print engine. Namely, from the turn-on to the turn-off of the power supply, most parts of the printing apparatus are energized.
However, in a printing apparatus having a relatively low frequency of use, the time in which the printing apparatus is actually operated is short relative to the energization time of the printing apparatus. The printer may sometimes be energized over night without being actually used and the printing apparatus unduly consumes power. Further, such continuous energization leads to the shortening of electric parts having limited durability.
On the other hand, the laser beam printer has been widely used as a computer output device because of its advantages of low price and compactness. As shown in FIG. 7, the laser beam printer comprises a printer engine section 90 for printing out characters on a photoconductor drum on the basis of dot data, and a printer controller section 80 for generating page information including dot pattern data based on the code data transmitted from an external host computer 70 and for sequentially sending out the dot pattern data to the printer engine 90.
As shown in FIG. 8, the printer engine 90 comprises an engine CPU 1, a low voltage supply (low voltage source ) 2, a high voltage supply ( high voltage source) 3, a scanner unit 4, a fixing unit 5, a main motor 6, a fan 7 and the like. As shown in FIG. 9, the printer controller 80 comprises a controller CPU 10, a RAM (DRAM) 30, a ROM 31, a memory I/O control section 32, a panel I/F control section 33, a host I/F control section 34, a console panel (operation panel) 35 and the like. A power supply voltage (e.g., +5 volts) necessary for the operation of the semiconductors of those sections is supplied from the printer engine 90. The engine CPU 1 of the printer engine 90 and the controller CPU 10 of the printer controller 80 always communicate to each other so that a status is transmitted from the printer engine 90 and a command is transmitted from the printer controller 80.
The controller CPU 10 receives the code data outputted from the host computer 70 through the host I/F control section 34, generates bit map image data based on the code data, and develops it on the RAM (DRAM) 30. When the code data includes text characters, font data corresponding to the text characters is read from a character generator (CG) formed on the ROM 31 to generate the bit map image data. When the generation of one page of bit map image data is completed, the controller CPU 10 requests the start of printing to the printer engine 90 and thereafter starts the printing by a vertical synchronization signal outputted from the printer engine 90.
In this case, the bit map image data developed on the RAM 30 is outputted to the printer engine 90 line by line in synchronism with the horizontal synchronization signal from the printer engine 90. The printer engine 90 generates various control signals based on the bit map image data to drive the scanner unit 4, the fixing unit 5, the motor 6 and the fan 7 and drive the laser beam sent from the printer controller 80 to print out the data.
In the prior art laser beam printer, since the RAM 30 in the printer controller 80 is usually a DRAM, it must be always refreshed in spite of the fact that it mainly reads and writes the data required in the printing. Further, the console panel 35 which is constructed by a liquid crystal touch panel (display panel) must always be illuminated. Further, since both the engine CPU 1 and the controller CPU 10 are clocked at a frequency close to a maximum processing speed of the CPU because a crystal oscillator (not shown) for generating the clock is designed by taking the highest speed condition into account. As a result, a large current is required during the printing as well as the stand-by.
When an end user uses the printing apparatus, there is a trend that the user dislikes the trouble for turning off the switch after the use. It is not rare that the stand-by status (stand-by for the image forming operation) occupies about 99% of the power-on period and the image formation operation occupies only the remaining 1%, depending on the manner of use of the apparatus. This causes a large amount of waste of power in the prior art laser beam printer. A similar problem occurs not only in the laser beam printer, but also in other image forming apparatus such as a conventional printer or the like.